What is MY - MId Year - it was less than mid year
There was a change in relatively early 1955 for all GM trucks:
Chevrolet trucks: from 1955st (first series) Advance-Design series to 1955nd (second series) Task Force series
GMC: from 1955 (first series) New Design (1955 Z series) to 1955 (second series) Blue Chip (1955 Y series)
The styles of the cabs changed significantly for Chevrolet & GMC.
